A mask device with blower according to the conventional technology has a blower attached to a front side or a rear side of a filtering material on a ventilation passage and helps breathing using an air supply force (inhalation force) of the blower. The blower is generally classified into a type (referred to as constant flow rate blower) where air is supplied at a steady flow regardless of breathing of a person who wears the mask device and a type (referred to as breathing dependant blower) where air supply is made following breathing of the person who wears the mask device.
An example of a mask device (breathing device) that includes a breathing dependant blower is disclosed in Japanese Patent No. 3,726,886 (Patent Document 1). In this mask device, an anterior portion of a face body is provided with an exhaust valve that is opened at the time of exhausting air and closed at the time of inhaling air, and an inhalation valve that is closed at the time of exhausting air and opened at the time of inhaling air. Furthermore, a motor driven blower that supplies external air to the face body through the inhalation valve during a normal operation is disposed. In the vicinity of the exhaust valve or the inhalation valve, a sensor composed of a photo interrupter is disposed, which detects a position of the exhaust valve or the inhalation valve and outputs a signal at the time of exhausting air or inhaling air. In addition, in accordance with the signal that is output from the sensor, power is supplied to the motor to normally operate the motor at the time of inhaling air, and power supply to the motor is stopped or reduced at the time of exhausting air.
The mask device with blower has an advantage that the person who wears the mask device comfortably inhales air as a first characteristic and a face body internal pressure becomes higher than an outer atmospheric pressure (becomes a positive pressure) as a second characteristic, and the mask device with blower can suppress harmful dust or harmful gas from being infiltrated due to a gap between a mask and a skin of the person who wears the mask device. In particular, the second characteristic is important. Accordingly, the mask device with blower is widely used for work for removing asbestos that has bad influence on the health of a human body even if an extremely small amount of harmful dust or harmful air is infiltrated into the human body and work in an environment where radioactive dust is provided (for example, in a nuclear power plant).
The mask device with blower has a disadvantage in that although air supply is sufficiently made when a filter is a new product, but the amount of air supply may be reduced due to dust clogging in a filtering material or a reduction in battery voltage. That is, if the mask device is continuously used, the amount of air supply is reduced, and the face body internal pressure cannot be maintained at a positive pressure. As a result, a harmful material may not be prevented from being infiltrated. Accordingly, if a positive pressure state in the face body can be easily recognized by a person who wears the mask device, a filter or a battery can be replaced immediately before or immediately after it turns a negative pressure, which results in continuously preventing the harmful material from being infiltrated.
The conventional technologies of detecting a face body internal pressure in a mask device are disclosed in Japanese Unexamined Patent Publication Nos. 10-28744 (Patent Document 2) and 60-68869 (Patent Document 3), and Japanese Unexamined Utility Model Publication Nos. 61-118618 (Patent Document 4) and 60-49851 (Patent Document 5).
The conventional technologies for detecting a face body internal pressure that are disclosed in Patent Documents 2 to 5 detect the face body internal pressure using a material that easily responds to a pressure of a diaphragm or the like. However, in order to allow the face body internal pressure to be detected even at a positive pressure of several Pascal, it is needed to make a corresponding pressure response more responsive. Since the diaphragm is very weak and may be easily deformed or destroyed, a failure or a setting deviation may be easily generated.
Meanwhile, a position (shape) of each valve in the face body is determined depending on a state of the face body internal pressure. Accordingly, by knowing the position (shape) of the valve, a positive pressure state of the face body internal pressure can also be recognized.